It is a known practice to use an atomized spray of electrostatically charged liquid to remove dust or similar fine pollutant particles from an atmosphere. These devices operate on the principle that the pollution particles remain suspended in the atmosphere in part because they carry an electrostatic charge. The liquid spray is inductively charged with a polarity opposite that of the pollution particles, with the result that the particles are attracted to the spray droplets and are thereby precipitated out of the atmosphere. Representative devices of this type may be seen by reference to at least U.S. Pat. Nos. 3,729,898 and 4,190,875, and the background discussions contained therein.
In typical devices of this type, a metallic ring electrode is positioned in a coaxial relationship around the tip of a spray nozzle. A suitable liquid, usually water, is discharged from the nozzle in the form of a high pressure atomized spray. As the spray passes the ring electrode, the atomized water particles are given a small electrostatic charge opposite in polarity to that of the ring electrode.
However, because of the high electrical potential required between the electrode and the nozzle, devices of this type present a shock hazard for humans. An even greater hazard arises if the device is employed in a potentially explosive environment, such as methane gas or vaporization fumes of highly flammable liquids. A single discharge arc between the ring electrode and the nozzle or surrounding structure could immediately ignite these materials. For the above reasons, devices of this type have not been widely used in potentially explosive environments, such a coal mines, even though the use of charged water sprays is known to be very effective in controlling coal dust.
In recognition of the extreme hazard presented by electrical arcing in a coal mine environment, a federal safety code for electrical equipment in coal mines has been developed under the authority of the United States Mine Safety and Health Administration. One of the mandatory design criteria for this equipment is that the high voltage areas of the equipment be shielded by a grounded metal housing. This requirement presents an obstacle to the use of inductively charged spray devices, since the ring electrode will not charge the spray particles if the electrode is encased in a grounded housing.
Accordingly, it is an object of the present invention to provide an inductively charged spray device with effective safeguards against electrical arcing so that the device may be used in a potentially explosive atmosphere. In addition, it is a further objective to provide such a device wherein the electrode is shielded by a grounded metal housing in compliance with the applicable federal mine safety codes.